Vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel. However, leaks in the emissions control system can inadvertently allow fuel vapors to escape to the atmosphere. Thus, various approaches are used to identify such leaks.
One such approach for leak detection includes sealing off the fuel tank, canister, and various conduits from atmosphere following engine shut-off and allowing pressure in the fuel system to build as heat is rejected from the engine to the fuel system. Fuel system degradation is then indicated if a rate of change of fuel system pressure is different than an expected change in pressure.
The inventors herein have recognized a few issues with the above approach. If the fuel system includes a fuel tank filled with low-volatility fuel, such as ethanol, sufficient pressure may not build in the fuel system due to the lack of vapors emitted by the ethanol fuel. Furthermore, if the vehicle is a hybrid vehicle, the engine may not generate sufficient heat to allow pressure to build in the fuel system.
Accordingly, embodiments are provided for detecting fuel system degradation without relying on generation of fuel system vapors. In one embodiment, a method comprises evacuating fuel from a first fuel tank to a second fuel tank, and indicating fuel system degradation in response to a change in fuel system pressure following the evacuation of fuel.
In this way, pressure may be built in the fuel system by evacuating fuel from the first tank to the second tank. When the fuel is evacuated, the resultant change in volume to the fuel tanks will cause a change in pressure that may be monitored to indicate fuel system degradation. In doing so, separate components for applying pressure may be dispensed with, saving engine packaging space and increasing engine efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.